Machines such as dozers, loaders, excavators, motor graders, and other types of heavy equipment use one or more hydraulic actuators to move a work tool. These actuators are fluidly connected to a pump on the machine that provides pressurized fluid to chambers within the actuators. As the pressurized fluid moves into or through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to affect movement of the actuator and the connected work tool. When the pressurized fluid is drained from the chambers, it is returned to a low-pressure sump on the machine.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the fluid draining from the actuator chambers to the sump often has a pressure greater than the pressure of the fluid already within the sump. As a result, the higher pressure fluid draining into the sump still contains some energy that is wasted upon entering the low-pressure sump. This wasted energy reduces the efficiency of the hydraulic system.
One method of improving the efficiency of a hydraulic system is described in U.S. Patent Publication No. 2003/0159577 of Pfaff that published on Aug. 28, 2003 (the '577 publication). In particular, the '577 publication describes a hydraulic system having five different electro-hydraulic valves connected between a variable displacement pump, a tank, and a tandem pair of boom actuators. A first of the valves controls pump flow to rod-ends of the boom actuators. A second of the valves controls flow from the rod-ends of the boom actuators to the tank. A third of the valves controls pump and tank connections with fourth and fifth valves. The fourth and fifth valves control independent flows into and out of head-ends of the boom actuator. The different valves of the hydraulic system are selectively controlled to produce an unpowered regenerative retract operation and a powered regenerative extend operation. During these operations, fluid is recycled between the head- and rod-ends of the boom actuators to reduce a load on the pump, thereby also reducing an amount of high-pressure fluid that is wasted during actuation and increasing an efficiency of the system.
Although the system of the '577 publication may have improved efficiency compared to a conventional hydraulic system, it may lack applicability. In particular, it may not be functional with a configuration having pilot-operated control valves or valves that control common functions associated with both head- and rod-ends of an actuator. In addition, the system of the '577 publication may not consider critical performance factors affecting regeneration during valve control.
The disclosed hydraulic control system is directed to overcoming one or more of the problems set forth above and/or other problems known in the art.